Minimizing environmental impacts of hydroelectric reservoirs through operational control: a generic approach to reservoirs in northern Quebec

A generic differential mass balance model has been posed for the calculation of the concentration of material released into the water column from inundated vegetation and soils as a function of several operational scenarios for the filling and emptying of reservoirs. Through comparison of surface, volume and flow rate parameters between reservoirs of the James Bay territory, it has been found that the maximum surface area of the land flooded, the maximum volume of water in the reservoir and the annual average turbined flow rate were strongly correlated. This allowed computation of all related parameters of the generic model through the specification of a single parameter. Application of the model to different latitudinal sites was done considering explicitly the characteristics of influent volumetric flow rate, water temperature and densities of the inundated phytomass and soils at these latitude and the respective kinetics for the release of material into the water column. Using the integral of concentration of organic carbon as a representative measure of the environmental impact, the results have indicated that the optimum times to initiate the filling operation and to initiate the subsequent emptying of the reservoir are relatively insensitive to parameters such as the residual volume of water in the reservoir and the residency time of the water in the reservoir. Also, these optimum operational parameters were found relatively insensitive to water temperature of the reservoir, influent volumetric flow rates or densities of the vegetation and soil components at the latitude at which a reservoir is sited. Selection of the optimum operational parameters reduced the concentration in the reservoir by 40–50% when compared to a simple filling operation as is done currently when creating a reservoir.